Female & Male BMI Calculator

What this BMI & TDEE calculator actually tells you

This tool estimates two important numbers:

• BMI (Body Mass Index) – a quick way to compare your weight to your height.
• TDEE (Total Daily Energy Expenditure) – an estimate of how many calories you burn in a day based on your body and activity level.

Together, they give you a simple snapshot of whether your current weight is in a healthy range
and roughly how many calories you need to maintain, lose, or gain weight.

⚠️ Important: This calculator is for general guidance only.
It can’t replace medical advice, a diagnosis, or a personalised plan from a doctor or dietitian.

How to use the calculator

1. Enter your age, sex, height, and weight.
2. Choose your activity level – be honest here.
   If you mostly sit during the day and only walk a bit, choose “sedentary” or “light”.
3. Click Calculate.
4. You’ll see:
   • Your BMI and BMI category
   • Your BMR (the calories your body uses at total rest)
   • Your TDEE (rough calories you burn on an average day)

You can then use the TDEE estimate as a guide for setting calorie targets:

• Slight deficit for fat loss
• Around TDEE for maintenance
• Slight surplus for weight gain

What is BMI?

Body Mass Index (BMI) is a simple calculation that uses your height and
weight to estimate whether your weight falls in a range that’s usually associated with lower health risk.

Formula (metric):
BMI = weight (kg) / (height (m))²

Example:
A person who weighs 70 kg and is 1.70 m tall:
BMI = 70 / (1.7 × 1.7) ≈ 24.2

BMI doesn’t measure body fat directly, but for most adults it’s a useful screening tool to flag
if further assessment might be helpful.

BMI categories for adults (20+)

These categories are based on World Health Organization (WHO) ranges and apply to most adults, men and women, aged 20 or older.

BMI categories for adults (20+)

These categories are based on World Health Organization (WHO) ranges and apply to most adults, men and women, aged 20 or older.

For most people, the long-term health risk is lowest in the 18.5–24.9 range, but this is only one piece of the puzzle. Genetics, muscle mass, health history, and lifestyle all matter too.

Risks of a high BMI (overweight & obesity)

A BMI in the overweight or obese range is linked to a higher risk of several health problems, especially when extra fat sits around the waist. These can include:

• High blood pressure
• Unhealthy cholesterol levels
• Type 2 diabetes
• Heart disease and stroke
• Osteoarthritis and joint pain
• Sleep apnoea and breathing problems
• Certain cancers (such as breast, colon, and endometrial)
• Lower energy, mobility problems, and reduced quality of life
• Higher risk of anxiety, depression, and body-image struggles

The goal is not to chase a “perfect” number, but to slowly move toward habits that bring your BMI and waist measurement into a safer range.

Risks of a low BMI (underweight)

Being underweight can also be a sign that your body isn’t getting what it needs. A low BMI can be associated with:

• Nutrient deficiencies and anaemia
• Low bone density and higher fracture risk (osteoporosis)
• A weaker immune system and more frequent infections
• Fertility and menstrual issues in women
• Delayed growth and development in children and teens
• Higher risk of complications after surgery
• Increased risk of illness or early death in some people

Sometimes underweight is due to illness, stress, trauma, eating disorders, or other underlying issues. If your BMI is low and you’re not sure why, it’s important to speak to a doctor.

Where TDEE fits into the picture

BMI tells you where you are right now in terms of weight relative to height.
TDEE (Total Daily Energy Expenditure) helps you understand what it takes to stay there or change it.

TDEE is calculated from:

• Your BMR (Basal Metabolic Rate) – the energy your body uses just to keep you alive (breathing, circulation, organ function)
• Your activity level – everything from walking around the house to gym sessions or a physically demanding job

Roughly:

• Eat around your TDEE → weight maintenance
• Eat a little below TDEE (300–500 kcal/day) → gradual, sustainable fat loss
• Eat a little above TDEE (250–300 kcal/day) → gentle weight gain, often alongside strength training

Crash dieting or extreme deficits may drop your weight quickly at first, but can also affect hormones, mood, sleep, and long-term metabolism – especially for women. Slow and steady really is kinder to your body.

Limitations of BMI (and why you shouldn’t obsess over the number)

BMI is a blunt tool. It’s useful, but it doesn’t tell the whole story.

It does not distinguish between:

• Muscle and fat
• Where fat is stored (hips vs. stomach)
• Body shape, ethnicity, or genetics

A few examples:

• A very muscular person can have a “high” BMI but low body fat.
• An older adult with low muscle mass may have a “normal” BMI but higher health risk.
• Different ethnic groups may experience health risks at slightly lower or higher BMIs.

That’s why it’s better to look at BMI alongside:

• Waist measurement
• Blood pressure, blood sugar, and cholesterol
• Energy levels, sleep, mood, and menstrual cycle (for women)
• Your own doctor’s feedback

For most South Africans, though, BMI plus waist size is still a simple and helpful starting point.

A gentle reminder

Numbers like BMI, BMR, and TDEE are just information – not a verdict on your worth, your body, or your progress.

Use this calculator to:

• Get a clearer picture of where you are
• Set realistic, kind goals
• Track changes over time as you build healthier habits

If your results worry you, or if you’re dealing with pregnancy, breastfeeding, chronic illness, or disordered eating, please chat to your healthcare provider or dietitian before making big changes.

Your body is not a maths problem to “fix”.
It’s your home – and small, consistent shifts in movement, food, sleep, and stress management can make a big difference over time.